1. Field of the Invention
This invention relates to valves for regulating fluid flows, and it more particularly relates to reciprocating gate valves.
2. Description of the Prior Art
The designs of valves have been well perfected for many years, and these designs are conformed to the type of flow control in which the valve is to be employed. One common commercial valve is the gate valve wherein a gate is reciprocated across a flow passage to regulate fluid flows.
The present invention concerns the gate valve with reciprocating gate such as used in high-pressure wellhead service. More particularly, this gate valve design is of parallel seats. The complementary gate parts have inclined plane devices which convert stem force to axial force for pressing the gate parts against the seats when the valve is adjusted into opened and closed position.
There are many gate valves available for wellhead service. Examples of these through conduit gate valves are the (1) W-K-M "Pow-R-Seal", (2) Gulfco API Gate Valve, (3) Demco type N, (4) Vetco Manual Gate Valve, (5) Gray Gate Valve Model 5, and (6) Newco Gate Valves. All valves of this type have removeable/replaceable seats, separate gate guide members to control gate reciprocation and closures (bonnet and lower cap). As a result, the valve body and gate guide members are relatively complicated in manufacture and as a result, greatly increase the costs of these gate valves.
In these gate valves of the through-conduit type, the gate assembly is always in contact with the seals to protect them from abrasion and corrosion, and also to keep the gate from vibration in fast fluid flows. When the valve is in opened position, the flow passes through a hole in the gate. The hole is usually of the same size as the flow passage in the valve body. With the valve in its closed position, an imperforate part of the gate rests between the seals and effectively blocks fluid flow through the valve body.
Because of the service requirements on wellheads, these valves have large safety factors in their design. As a result, the valves are heavy. For example, a 5000 psi model of 2 inch (i.e., of flow channel) will weigh about 150 pounds, and a 6 inch model will weigh about 1000 pounds.
The valve bodies on prior gate valves for use on wellheads have in general been forged or cast so as to obtain large number production cost advantages. Further, the dimensions of the closures etc., were determined previously on the necessary strength criterion for the valve. Stated in a different way, the diameter of flanges on the valve bore no relationship to the sizes of the sealing surfaces on the closures, gate assemblies, etc.
In the present gate valve, the valve body can be machined easily and completely starting with bar stock having a diameter equal to end connection flanges on the valve. The valve body has integral gate guides, and all annular sealing surfaces for the closures (bonnet and lower cap) have maximum diameters of fixed relationship to the flanges. With this arrangement, the annular bearing surfaces on the body are less than the bolting bearing surfaces on the closures.